Nanofiber technology has not yet developed commercially and, therefore, engineers and entrepreneurs have not had a source of nanofibers to incorporate into their designs. Uses for nanofibers will grow with improved prospects for cost-efficient manufacturing, and development of significant markets for nanofibers is almost certain in the next few years. The leaders in the introduction of nanofibers into useful products are already underway in the high performance filter industry. In the biomaterials area, there is a strong industrial interest in the development of structures to support living cells. The protective clothing and textile applications of nanofibers are of interest to the designers of sports wear, and to the military, since the high surface area per unit mass of nanofibers can provide a fairly comfortable garment with a useful level of protection against chemical and biological warfare agents.
Carbon nanofibers are potentially useful in reinforced composites, as supports for catalysts in high temperature reactions, heat management, reinforcement of elastomers, filters for liquids and gases, and as a component of protective clothing. Nanofibers of carbon or polymer are likely to find applications in reinforced composites, substrates for enzymes and catalysts, applying pesticides to plants, textiles with improved comfort and protection, advanced filters for aerosols or particles with nanometer scale dimensions, aerospace thermal management application, and sensors with fast response times to changes in temperature and chemical environment. Ceramic nanofibers made from polymeric intermediates are likely to be useful as catalyst supports, reinforcing fibers for use at high temperatures, and for the construction of filters for hot, reactive gases and liquids.
It is known to produce nanofibers by using electrospinning techniques. These techniques, however, have been problematic because some spinnable fluids are very viscous and require higher forces than electric fields can supply before sparking occurs, i.e., there is a dielectric breakdown in the air. Likewise, these techniques have been problematic where higher temperatures are required because high temperatures increase the conductivity of structural parts and complicate the control of high electrical fields.
It is known to use pressurized gas to create polymer fibers by using melt-blowing techniques. According to these techniques, a stream of molten polymer is extruded into a jet of gas. These polymer fibers, however, are rather large in that the fibers are greater than 1,000 nanometers (1 micron) in diameter and more typically greater than 10,000 nanometers (10 microns) in diameter. It is also known to combine electrospinning techniques with melt-blowing techniques. But, the combination of an electric field has not proved to be successful in producing nanofibers inasmuch as an electric field does not produce stretching forces large enough to draw the fibers because the electric fields are limited by the dielectric breakdown strength of air.
The use of a nozzle to create a single type of nanofiber from a fiber-forming material is known from co-pending application Ser. No. 09/410,808. However, such a nozzle cannot simultaneously create a mixture of nanofibers that vary in their composition, size or other properties.
Many nozzles and similar apparatus that are used in conjunction with pressurized gas are also known in the art. For example, the art for producing small liquid droplets includes numerous spraying apparatus including those that are used for air brushes or pesticide sprayers. But, there are no apparatus or nozzles capable of simultaneously producing a plurality of nanofibers from a single nozzle.
It is therefore an aspect of the present invention to provide a method for forming a plurality of nanofibers that vary in their physical or chemical properties.
It is another aspect of the present invention to provide a method for forming a plurality of nanofibers as above, having a diameter less than about 3,000 nanometers.
It is yet another aspect of the present invention to provide a method for forming a plurality of nanofibers as above, from the group consisting of fiber-forming polymers, fiber-forming ceramic precursors, and fiber-forming carbon precursors.
It is still another aspect of the present invention to provide a nozzle that, in conjunction with pressurized gas, simultaneously produces a plurality of nanofibers that vary in their physical or chemical properties.
It is yet another aspect of the present invention to provide a nozzle, as above, that produces a plurality of nanofibers having a diameter less than about 3,000 nanometers.
It is still another aspect of the present invention to provide a nozzle that produces a mixture of nanofibers from one or more polymers simultaneously.
At least one or more of the foregoing aspects, together with the advantages thereof over the known art relating to the manufacture of nanofibers, will become apparent from the specification that follows and are accomplished by the invention as hereinafter described and claimed.
In general the present invention provides a method for forming a plurality of nanofibers from a single nozzle comprising the steps of: providing a nozzle containing: a center tube; a first supply tube that is positioned concentrically around and apart from said center tube, wherein said center tube and said first supply tube form a first annular column, and wherein said center tube is positioned within said first supply tube so that a first gas jet space is created between a lower end of said center tube and a lower end of said supply tube; a middle gas tube positioned concentrically around and apart from said first supply tube, forming a second annular column; and a second supply tube positioned concentrically around and apart from said middle gas tube, wherein said middle gas tube and second supply tube form a third annular column, and wherein said middle gas tube is positioned within said second supply tube so that a second gas jet space is created between a lower end of said middle gas tube and a lower end of said second supply tube; and feeding one or more fiber-forming materials into said first and second supply tubes; directing the fiber-forming materials into said first and second gas jet spaces, thereby forming an annular film of fiber-forming material in said first and second gas jet spaces, each annular film having an inner circumference; and simultaneously forcing gas through said center tube and said middle gas tube, and into said first and second gas jet spaces, thereby causing the gas to contact the inner circumference of said annular films in said first and second gas jet spaces, and ejecting the fiber-forming material from the exit orifices of said first and third annular columns in the form of a plurality of strands of fiber-forming material that solidify and form nanofibers having a diameter up to about 3,000 nanometers.
The present invention also includes a nozzle for forming a plurality of nanofibers by using a pressurized gas stream comprising a center tube, a first supply tube that is positioned concentrically around and apart from said center tube; wherein said center tube and said first supply tube form a first annular column, and wherein said center tube is positioned within said first supply tube so that a first gas jet space is created between a lower end of said center tube and a lower end of said supply tube; a middle gas tube positioned concentrically around and apart from said first supply tube, forming a second annular column; a second supply tube positioned concentrically around and apart from said middle gas tube, wherein said middle gas tube and second supply tube form a third annular column, and wherein said middle gas tube is positioned within said second supply tube so that a second gas jet space is created between a lower end of said middle gas tube and a lower end of said second supply tube.